Internal combustion engines (ICE) may combust a mixture of air and fuel within one or more combustion chambers to produce a mechanical output. During the combustion, various exhaust gases are produced and expelled to the atmosphere. In some instances, a portion of the exhaust gas may be recirculated back into the engine cylinders (via an exhaust gas recirculation system). In a gasoline engine, this inert exhaust may displace an amount of combustible mixture in the cylinder resulting in increased engine efficiency. In a diesel engine, the exhaust gas may replace some of the excess oxygen in the pre-combustion mixture. In either instance, the recirculated exhaust may reduce the combustion temperature in the cylinder and/or reduce the creation of certain gaseous byproducts.
Internal combustion engines are often called upon to generate considerable levels of power for prolonged periods of time on a dependable basis. Many such ICE assemblies employ a supercharging device, such as an exhaust gas turbine driven turbocharger, to compress the airflow before it enters the intake manifold of the engine in order to increase power and efficiency.
Specifically, a turbocharger is a centrifugal gas compressor that forces more air and, thus, more oxygen into the combustion chambers of the ICE than is otherwise achievable with ambient atmospheric pressure. The additional mass of oxygen-containing air that is forced into the ICE improves the engine's volumetric efficiency, allowing it to burn more fuel in a given cycle, and thereby produce more power.
A typical turbocharger includes a central shaft that is supported by one or more bearings and that transmits rotational motion between an exhaust-driven turbine wheel and an air compressor wheel. Both the turbine and compressor wheels are fixed to the shaft, which in combination with various bearing components constitute the turbocharger's rotating assembly.